This invention relates generally to a damping system, and more particularly to a system for reducing vibrations at very low levels of motion.
In the field of very-long-range optical instruments, particularly in the case of optical instruments used on spacecraft, it is essential to reduce vibrations which can interfere with the operation of the optical instrument, since the performance of such instruments depends on maintaining the precision and stability of the instruments to within nanometers of the ideal shape of the instrument. Friction and freedom in the joints of deployed structures have the capacity to change the shape of the instrument at the micron and nanometer levels of resolution. These shape changes can induce low level transient shocks and persistent vibrations that perturb the instrument""s optics and reduce or destroy the quality of the scientific observation. These vibrations cause the departure of structures and mechanisms from ideal linear behavior with very small, often nanometer level, deformations.
In order to reduce or eliminate these vibrations, the optical instruments are mounted to damping mechanisms which are designed to damp out the vibrations so that they do not affect the operation of the instrument. The two types of systems which are currently used for precision instrument damping include active systems and passive systems. Active systems use a combination of actuators and sensors to create xe2x80x9canti-vibrationsxe2x80x9d that are intended to exactly cancel out the unwanted vibrations present in the system. While these systems can be very effective in damping low level vibrations, they tend to be very massive, complex and expensive to develop and operate. Furthermore, they require valuable spacecraft power to operate and, due to their increased complexity, are not extremely reliable or stable.
Passive systems use some form of physical behavior, such as material damping or turbulent fluid flow, to transform the vibrational energy into heat energy. While these systems are less complex and less expensive than active systems, they cannot currently provide the high performance of active systems; they cannot be reconfigured once the spacecraft is launched; and the performance of material or fluid based passive systems are very sensitive to the ambient temperature.
While friction in space structure joints has long been recognized as a dominant source of dissipation in precision structures, it has not been used as an intentional passive source of vibration damping. The three main reasons for this are: 1) it is difficult to predict and control the levels of damping due to friction in structural joints; 2) loss factors due to friction are generally limited to 1-5%; and 3) any dissipation due to friction can be accompanied by large nonlinearities in the structural dynamics, making the active control of the structure more difficult.
It is therefore an object of this invention to provide a system which effectively dampens vibrations.
It is a further object of this invention to provide such a system that is very effective at low levels of vibrational amplitude.
It is a further object of this invention to provide such a system which is passive and therefore requires no power source.
It is a further object of this invention to provide such a system which uses friction as a damping force.
It is a further object of this invention to provide higher levels of damping than is currently available in passive systems.
It is a further object of this invention to provide better damping at low levels of motion than is currently available in passive systems.
It is a further object of this invention to provide such a system which is not sensitive to temperature variations.
It is yet a further object of the invention to provide such a system which is simple and inexpensive to manufacture and use.
It is a further object of this invention to provide a system that does not introduce unwanted non-linear dynamics.
The invention results from the realization that a combination of frictional dissipative devices can be used to effectively dampen vibrations associated with optical instruments on spacecraft. The combination of frictional dissipative devices can be used to dampen vibrations in the vertical and horizontal planes of a mounting platform for a support strut of an optical instrument, which mounting plate is frictionally engaged by the frictional dissipative devices.
This invention features a damping system including a housing that receives vibrations, a mounting platform movably disposed with respect to the housing, at least one bearing surface on or attached to one of the housing and the platform and at least one frictional member on or attached to the other of the housing and the platform in contact with the bearing surface. The system frictionally dampens vibrations received by the housing and isolates the platform from vibrations.
In a preferred embodiment, the bearing surface may be flat and the frictional member may be spherical. The bearing surface may be disposed on the mounting platform and the spherical frictional member may be disposed on the housing. The housing may have first and second sets of opposing interior walls which cooperate to define a periphery of a cavity therebetween, the spherical frictional member being mounted to at least one of the walls of the first set of opposing interior walls. The mounting platform may be frictionally engaged with the spherical frictional member within the cavity, wherein the mounting platform may be adapted for mounting a support strut thereto. The damping system may further include a pair of opposing spherical frictional members, each mounted to one of the walls of the first set of opposing interior walls, and the mounting platform may be frictionally mounted between the spherical frictional members. Each of the walls of the first set of opposing interior walls may include a spring mechanism disposed between each wall and the associated spherical frictional member, for biasing each spherical frictional member against the mounting platform. The housing may further include a first plate and a second plate mounted in a perpendicular relationship to the opposed interior walls thereby defining a bottom and top, respectively, of the cavity. The second plate may include an aperture to allow the support strut to be mounted to the mounting platform through the second plate. The damping system may further include means for biasing the mounting platform between the first and second plates including spherical devices, which may be ball bearings, disposed between each of the first and second plates and the mounting platform. The second plate may be adjustably mounted to the housing, thereby enabling a bias force between the spherical devices and the mounting platform to be adjusted. Each of the spring mechanisms may include a leaf spring integrated into each of the walls proximate the spherical frictional member and the cavity and the mounting platform may be rectangular in shape. The damping system may further include means for maintaining the relative position of the spherical devices within the cavity.
This invention also features a damping system including a housing that receives vibrations, a damping platform movably disposed within the housing and means for isolating the platform from vibrations received by the housing. The isolating means includes a plurality of ball bearings mounted between the damping platform and an upper interior surface of the housing and a plurality of ball bearings mounted between the damping platform and a lower interior surface of the housing.
This invention also features a damping system for reducing vibration in an instrument having at least one support strut, the damping system a housing having first and second sets of opposing interior walls which cooperate to define a periphery of a cavity therebetween, a mounting platform disposed within the cavity, the mounting platform being adapted for mounting a support strut thereto and a spherical contact coupled to each of the walls of the first set of opposing interior walls in frictional engagement with the mounting platform for reducing vibrations transferred to the mounting platform by the housing.
In a preferred embodiment, each of the walls of the first set of opposing interior walls may include a spring mechanism which operates to bias each spherical contact against the mounting platform. The housing may further include a first plate and a second plate mounted in a perpendicular relationship to the opposed interior walls thereby defining a bottom and top, respectively, of the cavity, the second plate including an aperture to allow the support strut to be mounted to the mounting platform through the second plate. Four spherical devices, such as ball bearings, may be disposed between each of the first and second plates and the mounting platform. The second plate may be adjustably mounted to the housing, thereby enabling a bias force between the spherical devices and the mounting platform to be adjusted. The spring mechanism may include a leaf spring integrated into each of the walls proximate the spherical contact. The cavity and the mounting platform may be rectangular in shape, and the device may include a device for maintaining the relative position of the spherical devices within the cavity.